Installing Porcelain Tile
All porcelain tiles are ceramic, but not all ceramic tiles are porcelain. Porcelain tiles absorb virtually no moisture, and thus, can be used on exterior and wet-area surfaces, but not all porcelain tiles are alike. Available unglazed and glazed, unglazed porcelain tiles usually have a matte finish, but they may also be polished, and since the color runs through the entire body of the tile, unglazed porcelain field tiles make a good choice for commercial applications since there is no glaze to wear away. Unglazed porcelain tiles can also be profiled and polished into bullnose tiles, using the same tools and techniques that are employed to create stone bullnose tiles. And as you might expect, unglazed porcelain tiles usually have greater slip resistance than porcelain tiles that have been glazed.
For the best results, specify a porcelain tile that reflects the style, performance requirements, expectations and budget of the intended installation. The break and compressive strength of porcelain tiles (like other types of ceramic tiles) will vary from one tile to another. This is also true for maintenance requirements. Some porcelain tiles have a rather open surface finish. By open, I mean that the surface texture of the tile is relatively coarse compared to honed or polished tiles. This texturing is intentional, and is designed for high-traffic floors whose surfaces are frequently wet: food preparation or service areas, for example. Tiles in such areas usually undergo wet cleanings one or more times each day, so neither accumulation of dirt in the open pores of the tiles, nor the cleaning routine necessary to keep the tile surface clean is a problem. Using such tiles in a light residential application, though, should be avoided unless the building owner is apprised of the maintenance required to keep the tiles looking clean.
Regarding slip resistance, many highly polished 12-inch (and larger) porcelain tiles compare well against porcelain tiles that have been honed. If slip resistance is required, make certain the tile you specify meets the project requirements. The same properties that allow porcelain tiles to resist the penetration of moisture also tend to throw off any coatings applied to porcelain tiles to improve slip resistance or for aesthetics. In my opinion, you will get better results selecting a porcelain tile that meets the project requirements, rather than mess with a corrective coating. Most porcelain tiles designed for floor use are dense, strong, and highly resistant to moisture penetration - properties that make porcelain tiles somewhat difficult to bond.
Regular thinset mortar has been shown to produce relatively low strength when it is used to adhere porcelain tiles to a setting bed. The most likely reason for this is porcelain tile's ability to resist moisture penetration. For this reason, most porcelain tile manufacturers specify a latex thinset mortar as the bonding material, and I recommend using a premium latex thinset for installing porcelain tiles because latex thinsets offer improved bond strength over regular thinset mortars. Because large size (10 inches or larger) porcelain tiles tend to encapsulate moisture, latex thinset mortars may require additional curing time. For this reason, the specifications of some large-size porcelain tile installations may require the use of a rapid-setting latex thinset.
Organic adhesives (mastics) should be avoided under large-size porcelain tiles for two reasons. Lack of sufficient bond strength is the first, and inadequate curing is the other, especially if the setting bed has been covered with a waterproofing membrane: sandwiched between two impermeable surfaces (the porcelain tile and the membrane), moisture cannot evaporate from the organic adhesive and allow it to harden and cure. Even with very thin layers of mastic, the result is that only an inch or so of the mastic at the perimeter of the tile hardens while the remainder stays moist and incapable of adding any compressive strength to the installation. Even worse, should the perimeter band of hardened mastic re-emulsify because of contact with moisture, the strength of the installation can become further compromised. Broken tiles are the result.
According to tile industry specs, a 1/4-by-1/2-by-1/4-inch U-notched trowel is about the right size for a 12-inch porcelain tile to achieve the required 80 percent minimum uniform adhesive coverage for tiles installed in dry areas (95 percent is required for wet areas). This much organic adhesive beneath a porcelain tile will also result in uncured adhesive and a significant reduction of anticipated compressive strength.
Some installers rely exclusively on a wet saw for cutting porcelain tile. This is alright for L-shaped cuts, but unnecessary for straight cuts. Wet-cutting is slow and it requires that each tile cut be thoroughly dried off before setting in adhesive; otherwise, moisture will prevent a good bond. Some installers complain of erratic cutting with a traditional snap-cutter, but a narrow band of light oil applied to the scoring zone will result in a nice, clean cut with no moisture to ruin the bond; make sure you clean off residual oil before setting the tile.
For drilling small holes in porcelain tiles, I use a diamond bit designed for drilling holes in glass. For larger holes, I use a diamond core bit, and throw away the carbide pilot bit. Instead, I cock the bit to one side to start the hole, or use a bushing made from a scrap two-by-four. Always use water to get the most life from the drill.